Phosphorus limitation on CO_(2)fertilization effect in tropical forests informed by a coupled biogeochemical model

Tropical forests store more than half of the world's terrestrial carbon(C)pool and account for one-third of global net primary productivity(NPP).Many terrestrial biosphere models(TBMs)estimate increased productivity in tropical forests throughout the 21st century due to CO_(2)fertilization.However,phosphorus(P)liaitations on vegetation photosynthesis and productivity could significantly reduce the CO_(2)fertilization effect.Here,we used a carbon-nitrogen-phosphorus coupled model(Dynamic Land Ecosystem Model;DLEM-CNP)with heterogeneous maximum carboxylation rates to examine how P limitation has affected C fluxes in tropical forests during1860-2018.Our model results showed that the inclusion of the P processes enhanced model performance in simulating ecosystem productivity.We further compared the simulations from DLEM-CNP,DLEM-CN,and DLEMC and the results showed that the inclusion of P processes reduced the CO_(2)fertilization effect on gross primary production(GPP)by 25%and 45%,and net ecosystem production(NEP)by 28%and 41%,respectively,relative to CN-only and C-on ly models.From the 1860s to the 2010s,the DLEM-CNP estimated that in tropical forests GPP increased by 17%,plant respiration(Ra)increased by 18%,ecosystem respiration(Rh)increased by 13%,NEP increased by 121%per unit area,respectively.Additionally,factorial experiments with DLEM-CNP showed that the enhanced NPP benefiting from the CO_(2) fertilization effect had been offset by 135%due to deforestation from the 1860s to the 2010s.Our study highlights the importance of P limitation on the C cycle and the weakened CO_(2)fertilization effect resulting from P limitation in tropical forests.

The carrying capacity for vegetation of forest land across China:Near real-time monitoring and short-term forecasting based on satellite observation

Ecological restoration projects implemented over the past 20 years have substantially increased forest coverage in China,but the high tree mortality of new afforestation forest remains a challenging but unsolved problem.It is still not clear how much vegetation can be sustained by the forest lands with given water,energy and soil conditions,i.e.,the carrying capacity for vegetation(CCV)of forest lands,which is the prerequisite for planning and implementing forest restoration projects.Here,we used a simplified method to evaluate the CCV across forest lands nationwide.Specifically,based on leaf area index(LAI)dataset,we use boosted regression tree and multiple linear regression model to analyze the CCV during 2001-2020 and 2021-2030 and explore the contribution of environmental factors.We find that there are three typical regions with lower CCV located in the Loess Plateau and the southern region of the Inner Mongolia Plateau,the Hengduan Mountain region,and the Tianshan Mountains.More importantly,the vegetation in the regions near the dry-wet climate transition zone show excess local carrying capacity for vegetation over the past two decades and they are more susceptible to potential climatic stress.In comparison,in the Greater Khingan Mountains and Hengduan Mountains,there is high potential to improve the forest growth.Temperature,precipitation and soil affects the CCV by shaping the vegetation in the optimal range.This indicates that more consideration should be given to restrictions of regional environmental constraints when planning afforestation and forest management.This study has important implications for guiding future forest scheme in China.

Global methane and nitrous oxide emissions from terrestrial ecosystems due to multiple environmental changes

Greenhouse gas(GHG)-induced climate change is among the most pressing sustainability challenges facing humanity today,posing serious risks for ecosystem health.Methane(CH_(4))and nitrous oxide(N_(2)O)are the two most important GHGs after carbon dioxide(CO_(2)),but their regional and global budgets are not well known.In this study,we applied a process-based coupled biogeochemical model to concurrently estimate the magnitude and spatial and temporal patterns of CH_(4)and N_(2)O fluxes as driven by multiple environmental changes,including climate variability,rising atmospheric CO_(2),increasing nitrogen deposition,tropospheric ozone pollution,land use change,and nitrogen fertilizer use.The estimated CH_(4)and N_(2)O emissions from global land ecosystems during 1981-2010 were 144.39±12.90 Tg C/yr(mean 62 SE;1 Tg=1012 g)and 12.52±0.74 Tg N/yr,respectively.Our simulations indicated a significant(P,0.01)annually increasing trend for CH_(4)(0.43±0.06 Tg C/yr)and N_(2)O(0.14±0.02 Tg N/yr)in the study period.CH_(4)and N_(2)O emissions increased significantly in most climatic zones and continents,especially in the tropical regions and Asia.The most rapid increase in CH_(4)emission was found in natural wetlands and rice fields due to increased rice cultivation area and climate warming.N_(2)O emission increased substantially in all the biome types and the largest increase occurred in upland crops due to increasing air temperature and nitrogen fertilizer use.Clearly,the three major GHGs(CH_(4),N_(2)O,and CO_(2))should be simultaneously considered when evaluating if a policy is effective to mitigate climate change.

Climate extremes and ozone pollution:a growing threat to China’s food security

Ensuring global food security requires a sound understanding of climate and environmental controls on crop productivity.The majority of existing assessments have focused on physical climate vari-ables(i.e.,mean temperature and precipitation),but less on the increasing climate extremes(e.g.,drought)and their interactions with increasing levels of tropospheric ozone(O3).Here we quantify the combined impacts of drought and O3 on China’s crop yield using a comprehensive,process-based agricultural eco-system model in conjunction with observational data.Our results indicate that climate change/variability and O3 together led to an annual mean reduction of crop yield by 10.0%or 55 million tons per year at the national level during 1981-2010.Crop yield shows a growing threat from severe episodic droughts and in-creasing O3 concentrations since 2000,with the largest crop yield losses occurring in northern China,causing serious concerns in food supply security in China.Our results imply that reducing tropospheric O3 levels is critical for securing crop production in coping with increasing frequency and severity of extreme climate events such as droughts.Improving air quality should be a core component of climate adaptation strategies.

Methane emissions from livestock in East Asia during 1961−2019

Context:East Asia is a crucial region in the global methane(CH4)budget,with significant contributions from the livestock sector.However,the long-term trend and spatial pattern of CH4 emissions from livestock in this region have not been fully assessed.Methods:Here,we estimate CH4 emissions from 10 categories of livestock in East Asia during 1961-2019 following the Tier 2 approaches suggested by the 2019 Refinement to the IPCC 2006 Guidelines.Results:livestock-sourced CH4 emission in 2019 was 13.22[11.42-15.01](mean[minimum%maximum of 95-confidence interval]Tg CH4 yr-1,accounting for an increase of 231%since 1961.The contribution of slaughtered populations to total emissions increased from 3%in 1961 to 24%in 2019.Spatially,the emission hotspots were mostly distributed in eastern China,South Korea,and parts of Japan,but they tend to shift northward after 2000.Conclusion:It is necessary to use dynamic emission factors and include slaughtered populations in the estimation of livestock CH4 emissions.Regions including Northern China,Mongolia,and South Korea deserve more attention in future CH4 mitigation efforts.

Responses of global terrestrial water use efficiency to climate change and rising atmospheric CO_(2)concentration in the twenty-first century

Terrestrial ecosystems play a significant role in global carbon and water cycles because of the substantial amount of carbon assimilated through net primary production and large amount of water loss through evapotranspiration(ET).Using a process-based ecosystem model,we investigate the potential effects of climate change and rising atmospheric CO_(2)concentration on global terrestrial ecosystem water use efficiency(WUE)during the twenty-first century.Future climate change would reduce global WUE by 16.3%under high-emission climate change scenario(A2)and 2.2%under low-emission climate scenario(B1)during 2010–2099.However,the combination of rising atmospheric CO_(2)concentration and climate change would increase global WUE by 7.9%and 9.4%under A2 and B1 climate scenarios,respectively.This suggests that rising atmospheric CO_(2)concentration could ameliorate climate change-induced WUE decline.Future WUE would increase significantly at the high-latitude regions but decrease at the low-latitude regions under combined changes in climate and atmospheric CO_(2).The largest increase of WUE would occur in tundra and boreal needleleaf deciduous forest under the combined A2 climate and atmospheric CO_(2)scenario.More accurate prediction of WUE requires deeper understanding on the responses of ET to rising atmospheric CO_(2)concentrations and its interactions with climate.

Recent patterns of terrestrial net primary production in Africa influenced by multiple environmental changes

Terrestrial net primary production(NPP)is of fundamental importance to food security and ecosystem sustainability.However,little is known about how terrestrial NPP in African ecosystems has responded to recent changes in climate and other environmental factors.Here,we used an integrated ecosystem model(the dynamic land ecosystem model;DLEM)to simulate the dynamic variations in terrestrial NPP of African ecosystems driven by climate and other environmental factors during 1980-2009.We estimate a terrestrial NPP of 10.22(minimum-maximum range of 8.9-11.3)Pg C/yr during the study period.Our results show that precipitation variability had a significant effect on terrestrial NPP,explaining 74%of interannual variations in NPP.Over the 30-yr period,African ecosystems experienced an increase in NPP of 0.03 Pg C/yr,resulting from the combined effects of climate variability,elevated atmospheric CO_(2)concentration,and nitrogen deposition.Our further analyses show that there is a difference in NPP of 1.6 Pg C/yr between wet and dry years,indicating that interannual climatic variations play an important role in determining the magnitude of terrestrial NPP.Central Africa,dominated by tropical forests,was the most productive region and accounted for 50%of the carbon sequestered as NPP in Africa.Our results indicate that warmer and wetter climatic conditions,together with elevated atmospheric CO_(2)concentration and nitrogen deposition,have resulted in a significant increase in African terrestrial NPP during 1980-2009,with the largest contribution from tropical forests.